Current tall buildings have many elevator shafts, but each shaft only has one cab operating in that shaft with one or more counterweight cables attached to the top center of the cab. Therefore, only one cab services each floor throughout the entire hoistway, and the general public normally has access to every cab and every floor in the entire building. This situation leads to inefficiencies and dissatisfactions for building owners, developers, and operators who would like to construct many fewer hoistways and operate many more cabs in each hoistway. As land increases in value in desirable urban locations, the financial pressure to construct taller and taller buildings will also increase. Already over 15 buildings worldwide have been constructed with more than 100 floors each, and two or more of these buildings exceed 150 floors. If the number of elevator hoistways and associated lobbies in these and other very tall buildings can be minimized, and the number of elevator cabs that operate in such elevator shafts can be maximized, then the value, efficiencies and desirabilities of these very expensive tall buildings can also be maximized.
The current situation also leads to inefficiencies and dissatisfactions for companies or individuals that lease or own many adjoining floors in a tall building. Many of them would like their employees or occupants to be able to access all of their adjoining floors without having to take a public elevator between such floors. Most modern companies who lease or own multiple adjoining floors in a tall building would like to have one or more private elevators for the exclusive use of all of its employees and guests, for reasons of privacy, security, efficiency, and commonality. The same is true for tall residential buildings, where one individual or family leases or owns several adjoining floors. Many employees currently waste a lot of time, effort and their company's money by having to leave the company's premises, go out into a public lobby, wait for a crowded public elevator cab moving the entire length of a long hoistway, and then re-enter the company's premises on another floor, not to mention the return trip to the employees desk on the original floor. Company's secrets can also be compromised or lost during this process. Such private elevators for each of such companies or individuals have been either impossible to construct, impractical, inflexible, or extremely costly. As such, there is a need for multi-cab elevator systems that increase hoistway efficiency and maximize the usage of hoistway space within tall buildings. Such multi-cab elevator systems will of course require sophisticated computer control systems and programs that will determine, control and coordinate the motions, speeds, breaking, reservations, destinations, safety, and all other functions and operations of such elevator systems.